Polymerization of olefins by metallocene catalysts

Polymerization of olefins by
metallocene catalysts
Pasquale Longo
Università di Salerno
plongo@unisa.it
Molecular Machine
Ziegler – Natta catalysts building some
plastic materials
(Poly-ethylene, Poly-propylene, Poly-styrene, etc. etc.)
This ship is made of only synthetic materials!
USA production (1960-2000)
(1,000s of metric tons)
year 1960
LDPE
HDPE
PP
PS
PVC
560
70
450
590
1970
1980
1,923
3,307
728 1,998
468
1,655
1,075 1,597
1,413 2,481
1990
2000
5,069 7,042
3,780 6,333
3,773 7,139
2,273 3,104
4,122 6,551
production went from 1.7 billion tonsm in 1960
to a massive 30.1 billion tonsm in 2000
PP strength
- very low density
- high stiffness
-  good tensile strength
-  inertness towards acids, alkalis and solvents
-  cost advantage
-  good injection-molding characteristics
very suitable for the large-volume
cost- and weight-conscious markets
(automotive)
PP automotive applications
Battery cases
Bumpers
Exterior trim
Interior trim
Fuel tanks
Instrument panels
Under-the-hood applications
Wires and cables
1,700 components of 5,000
are made of plastics
10% of total weight.
60% of interior weight
Amminoacids
Ile
Ala
Leu
Ile
Phe
Glu
Trp
Ser
Gly
His
Ser Arg
Lys
Lys
Proteins
Glu
Pro
His
Leu Phe Arg Gly Trp Ala Ala Glu Gly His Leu Ile Pro Trp Arg Lys
Pro
Propylene
Poly-propylene
Input
(brick)
Linus :
Human machine
Output
(building)
Classic machine
(Linus Van Pelt)
Input
(amino-acid)
Pro
His
Lys
Gly
Trp
Ile
Ser
Rybosom :
Glu
Leu
Natural Machine
Arg
Phe
Ile
Pro
Arg
Pro
Arg
Pro
Ser
Arg
Pro
Arg
Ser
Arg
Ser
Gly
Gly
Gly
Gly
Gly
Ile
His
Trp
His
Ile
Ile
Lys
Trp
Ile
Lys
Trp
Lys
Trp
Phe
Phe
Ile Lys
Phe
Ile
Phe
IlePhe
Phe
Ile Ile
Ile Gly
Ser
Arg
Gly
Arg
Ser
Ser
Gly
Ser
Gly
Gly
Gly
Gly
Phe
Lys
Trp
IleLeuPro
Lys
Phe
IleIleTrp
Lys
Phe
IlePro
Phe
Ile Trp
Phe
Ile Ser
Ile Lys
Leu
Leu
Leu
Glu Gly His Gly
Arg
Lys
SerSer
Output
(protein)
Molecular Machine
(Rybosom)
Input
(propylene)
Ziegler Natta
Catalysts :
Artificial Machine
Output
(poly-propylene)
Molecular Machine
(Ziegler-Natta catalysts)
Catalysts for
plastic material
production
1953-1954
Winners of the
Nobel Prize
1963
http://www.nobel.se
Karl Ziegler
Giulio Natta
Only italian Nobel prize winner for chemistry !
The motivations for awarding the
prize to Natta
•  Natural and biological catalysts had
previously dominated the synthesis of
stereoregular polymers.
•  Prof. Natta ended this monopoly.
Propylene : INPUT
Poly-propylene : OUTPUT
Metallocene : tools
Propylene (CH2=CHCH3)
H
A
C
H3C
2
B
INPUT
1
C
H
H
The faces of propene are chiral
A chiral object does not
over-lay its mirror-image
Louis Pasteur - 1848
Mirror
A
A*
Chirality = asymmetry
Lord Kelvin - 1904
MILESTONES
REACHED
Overview, history (1)
  First report in September 1955 using “purple phases” of TiCl3 (α-TiCl3
and γ-TiCl3) and AlEt3 (higher activity) or AlEt2Cl (higher
stereoselectivity).
  Solvay 1973: Added TiCl4, which acted as a catalyst to convert βTiCl3 into an active phase of TiCl3 (higher activity due to smaller
particles).
Overview, history (2)
  Shell 1980: TiCl4 supported on MgCl2 in presence of AlEt3 or AlEt2Cl.
Active species still TiCl3 .
  Other remarks:
  Awarded Nobel price in 1963.
  1980’s: Process attributed to Robert Banks and J. Paul Hogan
Cerutti, L; International Journal for Philosophy of Chemistry, 1999 (5), 3-41
Mechanism
  Two complications
  Why Cl-vacancy?
  Why stereospecific?
Cossee-Arlman postulate (1964)
Structure of the catalyst, overview
•  Three phases of TiCl3
Color
Stucture
Activity
α-TiCl3
Purple
Hexagonal layered
structure
Isotactic
β-TiCl3
Brown
Needle structure
Little
stereospecifity
γ-TiCl3
Purple
Cubic layered
structure
Like α-TiCl3
Structure of the catalyst, overview
•  Schematic view of the structures of α-TiCl2, α-TiCl3 and ß-TiCl3
Structure of the catalyst, active site (1)
•  Cl-vacancies on the edges of the crystal.
•  Electron Microscopy: active sites are on the edges
•  Ti at the active sites in a square of Cl
Structure of the catalyst, active site (2)
•  Square makes an angle of
55° with the base plane.
-
•  Cl ’s not equivalent:
–  3 stuck in crystal
–  1 bound by 2 Ti3+
–  1 loosely bound (to 1 Ti3+)
•  Vacancy and L not
equivalent sites
Stereospecifity, bonding of propylene
V
L
V
F
=
Ti
B
B
B
F
Ti
V
B
L
=
Ti
Et
L
AlEt3
F
Ti
F
B
B
H3C
Et
CH2
F
HC
Ti
CH2
Two possibilities:
H3C
V
CH3
Ti
F
CH
CH2
1. Alkalyne moves back to vacancy
2. Alkalyne doesn’t move back
Et
V
Stereospecifity, Polymerization (1)
H3C
CH
H3C
V
Ti
F
CH
Et
Ti
CH
H3C
V
CH
H3C
V
Ti
CH2 CH2
H2C
CH2
F
H3C
F
Et
H2C
CH2
H3C
F
Et
H3C
R
CH2
Polymer moves back to vacancy  isotactic polypropylene
Et
HC
Ti
CH2
CH3
H3C
R
Stereospecifity, Polymerization (2)
CH3
CH3
H3C Et
F
V
CH
Ti
CH2
H2C
H3C
CH2
R
|
Ti
F
H3C
CH
H3C Et
HC
CH
H2C
CH2
Ti
V
F
H3C
R
Polymer doesn’t back to vacancy  syndiotactic polypropylene
Experimental: Some syndiotactic PP at -70°
CH2
CH3
HC
Et
Cossee s mechanism
R
R
X
X
X
C3H6
X
X
X
X
X
insertion
X
X
X
R
C3H6
X
X
X
X
X
R
The Polymerization reaction
C
Polymer
+ CH2=CH2
Zr
C5
C
C5
C5
C
C
Polymer
Zr
C5
C5
C
Polymer
C
Zr
Polymer
Zr
C5
C5
C
Polymer
C
Zr
C5
C5
Piet Cossee
1964
C5
Allegra said that …
CH 3
C*
CH 2
P
Zambelli found that ….
Steric control
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
a
C
C
C
C
C
C
C
C
b
C
C
C
C
C
C
Hydrocarbons monomers
Ethylene
Propylene
Styrene
Conseguence of Chirality
The right foot can only wear right shoes.
A
Better
(more reactive)
A*
Catalyst
Poly-propylene :
OUTPUT
Poly-propylene
Isotactic Polypropylene
*
*
*
*
Syndiotactic polypropylene
*
*
*
Atactic Polypropylene
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Poly-propylene
If only one face of propylene gives co-ordination
to the catalyst…
A
A
A
A
A
A
*
*
*
*
*
*
Isotactic Polypropylene
*
*
Poly-propylene
If propylene gives co-ordination to the catalyst alternatively
with one and the other face …
A
A
A
A*
*
A*
*
*
A*
*
*
*
*
Syndiotactic Polypropylene
*
Poly-propylene
If propylene can give co-ordination to the
catalyst with both the faces …
A
A
A
A*
*
A*
A*
*
*
*Atactic
* poly-propylene
*
*
*
Metallocenes :
Molecular Tools
How is a Z/N metallocene
catalyst made?
Ancillary
Ligands
+
Group 4
Metal
=
Metallocene
How is a Z/N metallocene
catalyst made?
The metal is of
group 4.
How is a Z/N metallocene catalyst
made?
Which are the
ligands ?
How is a Z/N metallocene catalyst made?
?
?
?
?
?
?
?
?
More than 10,000 ligands !
How is a Z/N metallocene catalyst
made?
?
?
Which are the
other ligands?
How is a Z/N metallocene catalyst
made?
x
x
Which are the
other ligands?
Activators
Al(CH3)3 + H2O
Al O
CH3
REPRESENTS A BREAKTHROUGH
B(C 6F5)3
(C 6H5)3C + B(C 6F5)4
-
(C6H5)2NH + B(C 6F5)4
-
n
Cation
[Cp2M(CH3)] + + [MAOX]-
Cp2MX2 + MAO
+
CH3
Zr
C5
C5
How is a Z/N metallocene catalyst
made?
Monomero
Monomer
Polimerochain
Polymer
Which are the
other ligands?
Zr
C5
C5
How is a Z/N metallocene
catalyst made?
Ethylene
Polyethylene
Which are the
other ligands?
Zr
C5
C5
How is a Z/N metallocene catalyst
made?
Polypropylene
Propylene
Which
are
the
other
ligands?
Zr
C5
C5
The Tools at work:
Fundamental reaction
The Fundamental reaction
A chain of Snoopy kennels
The Catalytic Cycle
Polymerization reaction
One monomer insertion is going on every
millionth of a second.
A metallocene has a very high reactivity: it
can give 10,000-20,000 monomers insertion
for macromolecules
A metallocene has a very high activity: 1 g of
metallocene can produce more than 1,000 kg
of polymer before it becomes inactive.
The Tools at work:
Formation of stereoregular
polymers.
Stereoregular polymers.
The Symmetry of the King of diamonds
(isospecific symmetry)
The Symmetry of the King of diamonds
(isospecific symmetry)
Better situation !
Growing chain
Growing chain
The Symmetry of the King of diamonds
(isospecific symmetry)
A*
Growing chain
A
Consequence of the Chirality
The right foot can wear only right shoes !
A
A*
Catalyst
The Symmetry of the King of diamonds
(isospecific symmetry)
A*
?
A
or
Growing chain
A*
?
Better
or
? situation!
Growing chain
A
?
The Symmetry of the King of diamonds
(isospecific symmetry)
A
A
Growing chain
Growing chain
?
The Symmetry of the King of diamonds
(isospecific symmetry)
+
=
Isotactic Poly-propylene
A metallocene having the same symmetry of the
King of diamonds produces an isotactic polymer.
Polymerization reaction as a
catalytic cycle.
C2 symmetric metallocene
chain
Mt
Mt
chain
m
m
m
m
m
m
m
Allegra
By utilizing C2 symmetric stereorigid metallocene Allegra’s
conclusion was verified and an isotactic polypropylene
was obtained. The two sites of cationic catalyst with the
C2-symmetry are homotopics, and perform isotactic
polymerization of propene. An eventual back-skip reaction
of the chain, before a following monomer insertion, does
not influence the polymerization stereochemistry .
chain
Mt
Mt
chain
How is a Z/N metallocene catalyst made?
?
?
?
?
?
?
?
?
More than 10,000 ligands
have been synthesized
Symmetry of Chess
(syndiospecific symmetry)
Symmetry of Chess
(syndiospecific symmetry)
Better situation
Growing chain
Growing chain
Symmetry of Chess
(syndiospecific symmetry)
A*
?
A
or
Growing chain
A*
?
Better
?situationor !
Growing chain
A
?
Symmetry of Chess
(syndiospecific symmetry)
Growing chain
Growing chain
Symmetry of Chess
(syndiospecific symmetry)
A
A*
Growing
Growing
chain
Growing chain
chain
Growing chain
?
symmetry of Chess
(syndiospecific symmetry)
+
=
Syndiotactic Poly-propylene
A metallocene having chess symmetry produces a
syndiotactic polymer
Cs Symmetric Metallocene
chain
chain
Mt
r
Mt
r
r
r
r
r
r
The comparison of the symmetries
King of diamonds
Growing chain
Chess
Growing chain
Mechanism….
The syndiospecificity of catalysts having
Cs - symmetry was the first experimental
evidence that Cossee’s chain migratory
insertion was operative.
chain
Mt
chain
Mt
Mechanism …
Occasional meso (m) diads defects provide
evidence for back-skip reactions of the chain,
according to the hypothesis of Cossee and
Arlman which suggested that “the growing
alkyl group moves back to its original position
after each incorporation of a new monomeric
unit”.
r
r
m
m
r
r
r
Mechanism of Cossee and Arlman
R
R
X
X
X
C3H6
X
X
X
X
X
insertion
R
X
X
X
back -sk ip
X
X
X
X
X
R
Cossee and Arlman
The presence of tert-butyl group forbids the growing chain to
be located in the inward position , close to tert-butyl group,
thus, after each monomer insertion, the growing chain skips
back to the less crowded outward position. Hence, insertion
always takes place with the same face, because it occurs each
time on the same site of the catalyst that becomes isospecific.
chain
Mt
m
m
m
m
m
m
m
Summary….
Metallocenes are molecular tools that change input
molecules (alkenes) into output molecules (polymers).
Monomer
Polymer
Ethylene
Polyethylene
Propylene
Polypropylene
Summary….
Metallocenes are intelligent and change prochyral monomers (propylene) into stereoregular
polymers (polypropylene iso- or syndiotactic)
Monomer Symmetry
King of Diamonds
propylene
Chess
Polymer
isotactic polypropylene
syndiotactic polypropylene
Possible polypropylene from metallocenes:
ZrX 2
atactic polypropylene
ZrX 2
isotactic polypropylene
ZrX 2
syndiotactic polypropylene
ZrX 2
TiPh 2
ZrX 2
hemisotactic polypropylene
isotactic block polypropylene
atactic - isotactic
block polypropylene
C1 Symmetric Metallocene
chain
chain
Mt
R or S
R
Mt
R or S
R
R or S
R
R or S
R
Elastomeric polypropylene
+
Zr
P
+
Zr
P
2-(1-cyclopentadienyl)2-(1-phenyl)propano titanium
trichloride
(CH3))22C(Cp)(Ph)TiCl
(CH
C(Cp)(Ph)TiCl
3
3
+ MAO
atattico
atactic aatTT==50°C
50°C
Propylene
Isotactic at T = - 60°C
(CH3)2C(Cp)(Ph)TiCl3
[m]=0.76
Cp2TiCl2
[m]=0.85
CpTiCl3
[m]=0.51
Longo, P.; Amendola, A.G.; Fortunato, E.; Boccia, A.C.; Zambelli, A.; Macromol. Rapid
Commun. 2001, 22, 339.
Active specie
+
Ti
P
high temperature
Longo, P.; Amendola, A.G.; Fortunato, E.; Boccia, A.C.; Zambelli, A.; Macromol. Rapid
Commun. 2001, 22, 339.
+
Ti
low temperature
P
2-(1-indenyl)2-(1-naphtyl)propano
zirconium trichloride
CH3
CH3
C
ZrCl 3
+
MAO
Hapto-flexible catalysts
C. De Rosa, F. Auriemma, G. Circielli, A. C. Boccia, P. Longo Macromolecules, 36, 3465, 2003
Ethylene-Propylene Rubber
Common uses:
Automotive applications
Roofing membrane
Oil additives
Wires and cables
44%
18%
10%
8%
(Gaskets, seals,
Other
coated fabric,
footwear, rug underlay)
20%.
THE END